There are a number of applications, particularly within the auto industry, for an inexpensive and simple device which could discern between relatively smooth applied loads (e.g., torque, force, stress, strain, displacement) and irregular or varying such loads. In anti-lock braking (ABS) systems, for instance, foot pressure on the pedal should be steady for best braking performance. Many people have, however, been trained to "pump" their brakes when sliding. Pumping of the brake pedal in ABS systems therefore reduces, in some instances drastically reduces, brake performance. Hence, there is a need for a simple, inexpensive means for discerning between pumping (varying) loads and more steady foot force loads on the brake pedal. With this discernment, the ABS system electronics could automatically adjust the braking system response to compensate for any pumping action applied by the vehicle operator. The present invention, as will be shown, provides a method and apparatus for sensing and discerning between relatively uniform and irregular foot pressure loading applied by the operator.
Another suitable application involves automotive vehicle or other types of suspension systems. As an automobile hits bumps or other irregular road surfaces, it exhibits sudden changes in orientation which are related to the rapidly varying force loads being transmitted through the suspension systems. It is possible, however, in modern suspension systems, to provide computer control to the system which can effectively smooth out the rapid force variations induced in the wheels by the road surface before such forces are transmitted through to the vehicle compartment and the passengers. These "active" suspension systems use sophisticated electronics to make near instantaneous adjustments to various physical parameters of the system, and thereby smooth out the force variations. To do so, however, such systems need a means to distinguish between rough roads (rapid force variations) and smooth roads (relatively uniform force with little variation). As will be seen, the present invention comprises a simple method and apparatus to make such a distinction.
Misfire detection is another application for discernment of rapid force variations. (See later extensive discussion relating misfire detection to torque variations.) A sensor placed on or in the structure near or under a given cylinder would experience different force variations for a normal or abnormal cylinder firing. The methods shown hereinbelow to detect misfire, knock, or engine roughness due to torque variations may be used according to the present invention thereby for force (or stress/strain) variations to the same end.
Detection of cylinder degradation over time in internal combustion engines is yet another long felt need. As discussed below the present invention may be used to detect such degradation by monitoring lower torque production from cylinders which have lost power over time due to wear, ring damage, cylinder wall deterioration, or other causes.
Prior art methodologies for discerning load variations invariably entail load cells, typically employing strain gages, to make precise measurements of the load. An accurate, repeatable, mathematically explicit, correlation exists between the load being measured and the signal produced by the sensor (strain gage, transducer, etc) which monitors the load. Since the actual load is known to good accuracy, it is a simple matter to detect and flag load variations. The present invention, on the other hand, permits the effective use of a sensing system, such as a magnetostrictive sensing system, which for various "real world" physical reasons, may not be capable of providing an accurate correlation between load (as typically measured in pounds, pound-feet, psi, inches, inches per inch, etc) and sensor output (typically volts, milli-volts, milli-amps, etc).
Prior art configurations do not have the durability required for long term automotive and other application uses. For example, a strain gage mounted externally on a suspension system component such as a spring would have essentially zero probability of lasting even 10,000 miles, let alone the 100,000 miles modern day automotive manufacturers are demanding. Still further, such gages are virtually impossible to apply consistently and successfully in a mass production environment. Additionally, such sensing systems are vulnerable to temperature variations, and would be quite costly.
The present invention, as will be seen below, solves all of these prior art force variation sensing problems in a simple, inexpensive, and elegant manner, and does so in a unique and heretofore unprecedented way.
Further, the present invention may be employed to determine significant variations, not just of force, but of torque, stress, strain, deflection, and the like as well. A particularly useful application comprises misfire detection monitoring in automotive engines. It and other internal combustion engine torque variation applications are discussed in the ensuing paragraphs.
Two primary objectives of automobile engine control systems are to maximize engine performance, such as power for passing, etc., and to minimize fuel consumption. Rough running engines affect both power output and fuel economy adversely. On-board monitoring and control systems should be able to detect and, in some instances, correct for such roughness. Roughness may be due to incomplete burning of fuel in one or more cylinders. Extreme engine roughness occurs during cylinder misfire, that is, when no fuel is burned in one or more cylinders. Misfire can occur for several reasons, including lack of spark from the ignition system, malfunctioning of the fuel injection system, lack of sufficient air intake, faulty valves, etc.
While detection of roughness and misfiring during vehicle operation is highly desirable from the standpoints of performance and fuel economy, it has significant environmental impact as well. Incomplete burning of fossil fuels is a prime source of air pollution. An engine which misfires only 2% of the time, for example, may produce pollutant levels which exceed emission standards by 150%.
Governmental regulations covering emissions caused by cylinder misfire are being proposed. For example, the state of California has already notified automobile manufacturers that beginning with the 1994 model year, vehicles sold in California must have on-board means for detecting and warning of cylinder misfire. Such means must be capable of identifying which particular cylinder is misfiring, or in the case of multiple cylinder misfire, indicating that more than one cylinder is misfiring. California regulators have also stated they would prefer a system which could additionally: determine precisely which cylinders are misfiring in the case of multiple misfires; identify sporadic, non-periodic misfiring events; detect isolated misfires occurring a small percentage of the time, for example, 5 or fewer misfires for every 1,000 firings; and function properly under all engine speeds and driving conditions. Other states, as well as the U.S. Environmental Protection Agency, have indicated that they may issue cylinder misfire regulations similar to those proposed for California.
Prior art devices for roughness and misfire detection in internal combustion engines have utilized several different approaches. For example, the measurement of rotational speed (RPM) fluctuations is disclosed in U.S. Pat. No. 4,843,870 to Citron et al., and U.S. Pat. No. 4,932,379 to Tang et al.; and SAE papers #900232 by Plapp et al., #890486 by Citron et al., and #890884 by Rizzoni.
Detecting roughness and misfire has also been attempted by determining the absence of a spark in the ignition system as disclosed in U.S. Pat. No. 4,886,029 to Lill et al. and U.S. Pat. No. 4,928,228 to Fujimoto. The spark plug has also been used as a plasma probe as described in Johnson and Rado, "Monitoring Combustion Quality in Internal Combustion Engines Using Spark Plug as s Plasma Probe," IEEE Transactions on Vehicular Technology Vol VT-24, No 2, May 1975.
Sensing temperature at the exhaust port of each cylinder is disclosed in U.S. Pat. No. 3,939,711 to Hanaoka. Using non-magnetostrictive torque sensing and speed measurements is disclosed in SAE paper #890485 by Mauer et al. A generic torque sensor and comparison of mean or maximum versus minimum torque signals (and typically other signals such as RPM, accelerator depression level, etc.) to expected values stored in computer memory, is disclosed in U.S. Pat. No. 4,606,005 to Ribbens, and U.S. Pat. No. 4,940,030 to Morikawa. Monitoring exhaust chemistry, such as with a Lambda oxygen sensor in the exhaust flow, is taught in SAE paper #900232 by Plapp et al.
Each of these prior art approaches has disadvantages and it is likely that none may meet the strict standards that the California regulators and others seek. For example, rotational speed fluctuation detection is computationally intensive, and may be limited to engine speeds below 3500 to 4000 RPM, and has difficulty detecting non-repetitive misfires. Moreover, engine speed detection is subject to false alarms for vehicles operating on rough roads. A rough road will induce speed changes into the engine driveline at the drive wheels, irrespective of any engine misfire. These road induced speed changes will effectively mask the changes in speed that may be caused by engine misfire.
Detecting the absence of a spark will not detect misfire if the misfire is caused by fuel injection, valve, or other mechanical malfunctions. Plasma probing, temperature sensing, and exhaust gas chemistry sensing are all too slow and, heretofore, impractical for detecting low percentage misfire states. Further, exhaust gas sensing cannot identify which cylinder, or cylinders, are faulty. Torque sensing using non-magnetostrictive torque sensors are typically too large and unwieldy--often also requiring two or more monitoring locations along the crankshaft. Non-magnetostrictive torque sensors, such as strain gauge torque sensors, are impractical for mass production and extensive usage. U.S. Pat. Nos. 4,606,005 and 4,940,030 disclose using generic torque sensors; however, to the best of Applicants' knowledge, no such sensors currently exist which have proven suitable for automobile engine torque on-board monitoring.
A number of researchers have attempted to develop magnetostrictive torque sensors. Magnetostrictive torque sensors take advantage of the magnetostrictive property of ferromagnetic materials whereby tension stress in the material causes an increase in an induced magnetic field B in the material. Compressive stress causes a decrease in the induced magnetic field B. Typically an alternating current carrying coil is used to induce the magnetic field B into a ferromagnetic torque transmitting shaft. A secondary pickup coil, or other means, then monitors the change in the induced magnetic field B as the stress of the shaft changes with torque. The voltage signal generated across the secondary coil is an indicator of the torque. Specific geometry and the number of coils may vary for different magnetostrictive torque sensor designs, but the underlying principle is the same.
Typical magnetostrictive torque sensors are disclosed in U.S. Pat. No. 4,760,745 to Garshelis; U.S. Pat. No. 2,912,642 to Dahle; U.S. Pat. No. 4,414,856 to Winterhof; U.S. Pat. No. 4,589,290 to Sugiyama; U.S. Pat. No. 4,697,459 to Nonomura et al.; U.S. Pat. No. 4,939,937 to Klauber et al.; and application Ser. No. 07/518,083 to Klauber et al. The sensor disclosed in U.S. Pat. No. 4,760,745, for example, is a four solenoidal coil design which is inherently larger and is, therefore, typically more expensive and less suited for automotive application than the other types of magnetostrictive torque sensors. The other sensors may be miniaturized and are less expensive, but are limited by the random anisotropic variations in magnetic permeability of the iron and steel materials used in production crankshafts and driveshafts. These variations are inherent in the material and distort any measured induced magnetic field changes thereby resulting in inaccuracies and prohibiting the instantaneous monitoring of the power variations for individual cylinder misfiring or firing events.
In U.S. Pat. No. 4,716,773 and SAE paper #870472, Nonomura et al. show a cross design (two coil) magnetostrictive stress detector utilizing a phase adder circuit which adds a signal derived from the input voltage of the exciting coil to the filtered output signal from the pickup coil. The added signal is derived by shifting the phase and altering the amplitude of the input voltage. By adding this derived signal to the output voltage in the appropriate manner, the resulting signal is linearized (i.e., the relationship between output voltage and stress is made more linear). As shown herein, one embodiment of the present invention accomplishes the same end by different means not requiring the amplitude regulator or phase shifter needed by Nonomura et al. Further, the present invention is not limited to cross design magnetostrictive sensors. As will be seen the present invention has still other advantages, such as correction of overmodulation, not shown by Nonomura et al.
Applicants are currently unaware of any system for roughness or misfire detection which is completely satisfactory. Moreover, Applicants are unaware of any system which may satisfy more stringent environmental regulations, such as those pending in California.
The present invention may also be suited for a number of other uses. For example, during engine knock, the fuel in the cylinder ignites at an earlier point of the firing cycle and lasts for a much shorter period of time. When knock occurs, the combustion process is typically over near the point at which normal combustion would be just beginning. The torque pulse delivered during knock is therefore much shorter in width, different in magnitude, and located at a different location with respect to top dead center (TDC). Hence, comparison of signals such as those described herein to determine misfire or roughness can be used in similar fashion to determine knock.
Other uses according to the present invention include anti-lock braking wherein obtaining of peak braking torque is critical. By using the methodology shown herein, comparison of signals generated at the same or different points on a shaft.backslash.wheel system can result in a relative indication of torque, i.e., even though the actual value for torque may not be determined, it may be possible to determine when the maximum amount of torque is occurring. Feedback systems would then automatically seek the maximum signal, thereby maximizing braking torque, without actually having to determine the precise value of the torque. Similar logic holds for traction control systems wherein maximum traction torque is desired. Additionally, such comparisons of signals may be used in transmissions to facilitate smooth shifting without sudden torque shifts. Smoothness of torque transitions may be obtained, again without necessarily having to determine the actual value of the torque. Still other applications include bearing and I.C. engine cylinder degradation, machine tool monitoring, electric motors, generators, and any other devices wherein comparison of signals is at least partially dependent on torque may be useful.